Cannot wrap between workspaces using mouse, in some directions only

Hi,

I searched the web, the forums ect. but didn't find someone with this problem, so here I am:

I just installed Debian Wheezy and because of that switched from gnome to xfce. I have setup four workspaces, as 2x2 tiling. Switching between them works using the keys (ctlr+alt+[up|down|left|right]). Switching also works using the mouse, when going out of the current workspace towards the right and the bottom. However, it does _not_ work towards the left and the top. Eventually going in the opposite direction gets me to where I want to go, but it is really annoying to drop out of my current workspace 'by accident' by moving the mouse a little too close to the edge and then not being able to quickly go back by moving the mouse in the opposite direction. What _is_ odd is that switching using the mouse _does_ work if I drag a window around - in all four directions. I have no idea where or even how to look for a solution to this.

Some information about this system:

XFCE 4.8.1-1 (Debian Wheezy)one screen (no dual setup)2 rows in workspace switcher4 workspaces in total with no margins in either direction"wrap workspaces depending on the actual desktop layout" enabled. Disabling this doesn't help with my issue."wrap workspaces when the first or the last workspace is reached" is disabled. Enabling this doesn't seem to have any effect. It always does a complete loop towards the right and bottom (arriving at the start again), but not in the other directions.